Process and apparatus for the preparation of metallic salts



1934- .w. P. HEINEKEN ET AL 47,006

Patented Feb. 13, 1934 PATENT OFFICE PROCESS AND APPARATUS FOR THE PREP- ARATION OF METALLIC SALTS William P. Heineken, Dongan Hills, and Meyer L.

Freed, New York, N.

Y., assignors to Rufert Chemical Company, Dover, Del., a corporation of Delaware Application February 14, 1931. Serial No. 515,781

9 Claims.

This invention pertains generally to electrolytic processes. It pertains more particularly to the recovering, refining, or segregation of metals, as well as to the manufacture of metallic salts.

The invention is especially applicable to the recovery of metals from scrap alloys, but is also applicable in other ways.

Scrap metal may contain any one or more of the following metals: copper, iron, manganese, chromium, lead, arsenic, antimony, bismuth, nickel, cobalt, cadmium, tin, zinc, molybdenum, titanium, tantalum, gold, silver, platinum, ruthenium, palladium, rhodium, iridium, etc. For the purposes of illustration the invention will be described in connection with the production of metallic salts from the metals occurring in scrap, the process for this purpose including the refining of certain of such metals. It is understood, however, that the invention is in no way limited thereto.

The scrap is cast, stamped or otherwise formed into a shape suitable for use as an anode in anelectrolytic cell. The electrolytic cell is divided into an anode compartment and a cathode compartment. The division between the compartments comprises a'pervious diaphragm, which may be of special construction, or other similar means. The arrangement is such that regardless of the number of different metals and impurities present in the anode and in solution in electrolyte in the cathode compartment is kept substantially free from ions which under normal conditions would travel fromthe anode to the cathode. Ions are free to travel from the oathode to the anode, however, and upon liberation at theanode the atoms combine with the metals of the anode to form metallic salts.

The salts which are insoluble in the electrolyte of the anode compartment precipitate as slime at the anode, and the salts which are soluble in this electrolyte go into solution. By keeping the electrolyte in the cathode compartment substantially pure the metal of this electrolyte is deposited on 3 the cathode in a highly purified state.

, compartment of a higher density, or by applying pressure to the electrolyte in the cathode compartment, or otherwise. The replenishment of the electrolyte in the cathode compartment, therefore,-is not only for the purpose of maintaining a substantially uniform concentration of this electrolyte, but also to replace the liquid which difiuses into the anode compartment. Removal and replenishment of the electrolyte in the anode compartment is to guard against an undesirably high concentration of this electrolyte. The electrolyte in the anode compartment has a number of metallic salts in solution, and as the process proceeds there would be a tendency to build up a relatively high ion concentration.

By placing a supplementary cathode in the anode compartment it is possible to selectively separate the metals of the anode electrolyte by maintaining the electrolyte in the anode compartment in a condition suitable for such selective separation. It'is, of course, understood that the cathode electrolyte is in a condition suitable for the separation of the metal of such electrolyte.

While a single diaphragm between the compartments is suitable, we may, in some instances, preier to employ a double diaphragm and to circulate a suitable solution between the diaphragms. This would tend to neutralize electrolyte and carry away any ions which might, due to accidents or other causes, find their way through the diaphragm which holds back the anode electrolyte and the ions therein.

In the drawing like reference characters denote like parts throughout the various figures.

Figure 1 is a diagrammatic illustration in plan of an electrolytic cell embodying the invention.

Figure 2 is an elevation partly in section of the same.

The drawing illustrates the invention diagrammatically and is merely for the purpose of illustration. 95

At 10 is shown a tank which should be of a construction suitable for its purpose. 11 is a box or other device disposed within the tank 10. Box 11 is shown with a closed bottom 12, an open top 13, closed walls 14 and 15 and pervious walls 100 16 and 17. It can, of course, have any other suitable construction.

Cathode 18 is shown disposed within the box 11. Anodes are shown at 19 and 20, and supplementary cathodes at 21 and 22. An overflow 105 from box 11 is shown at 23, and an overflow from tank 10 is shown at 24.

For special purposes, to be hereinafter described, a box or other device 25, similar in construction to box 11, but of lesser dimensions, 110

may be disposed within the box 11. This box is spaced from the walls of box 11 so as to form spaces 26 between box 25 and box 11. Box 25 may also have any other suitable construction.

The following specific example of the opera tion of the invention is given merely for the purpose of illustration and it is understood that the invention is in no way limited thereto.

Let it be assumed that the electrolyte for starting is nickel sulfate solution having a concentra tion of 4% to 5% metallic nickel. If relatively pure nickel is to be deposited on the cathode it is, of course, obvious that the cathode electrolyte should be a substantially pure solution of nickel sulfate. On the other hand the-nickel sulfate solution comprising the anode electrolyte may be of any degree of purity, or this electrolyte for starting may be sulfuric acid alone.

Let it be assumed that the anode obtained as above described, is of unknown composition, ex cept that the presence of nickel and copper is known. When a suitable current is passed through the cell the following reaction takes place.

The pure nickel sulfate comprising the cathode electrolyte dissociates into ions of nickel and sulfate. The nickel is deposited on the cathode 18 and the sulfate ions travel outwardly through the walls 16 and 17 of box 11 to the anodes 19 and 20. sulfates of the soluble metals contained in the scrap are formed. All insoluble matter, including the insoluble salts formed at the anode, drops out and forms anode slime. Of all the possible metals present in the anodes thus obtained practically only iron, copper, cobalt and nickel would remain as soluble sulfates in the electrolyte. Precious metals being insoluble, are also carried down in the slime.

The following is a'list of reactions that apparently take place:

Iron remains in solution and is removed as a basic carbonate in a purification process to be hereinafter described.

A portion of any manganese will be in solution and this portion will be recovered with the iron. The remainder of the manganese will be found in the slime where it is thought to exist as a hy-' drated oxide.

Chromium will be found in the slime where it is thought to exist as an oxide.

Lead drops out as a sulfate.

Arsenic drops out as insoluble arsenate.

Antimony drops out as an insoluble basic sulfate.

Bismuth drops out as an insoluble basic sulfate.

Tin drops out as an insoluble basic sulfate.

If the anode has not been made by casting, zinc and cadmium remain in solution and are recovered as carbonates in the purification process. If the anode has been made by casting, both zinc and cadmium will have volatilized, and are recovered in the flue dust.

If the supplementary cathodes 21 and 22 are not used the overflow from the anode compartment may comprise a solution of iron, copper, cobalt and nickel sulfates. If the supplementary cathodes are used one of these metals might be deposited (upon the supplementary cathodes) if the proper conditions prevail. For instance, if the anode electrolyte is slightly acid, containing about 1% or more of free sulphuric acid, and a proper current density maintained, copper may be deposited at the supplementary cathode.

Nickel deposits best from a neutral solution.

The pure nickel sulfate solution of the cathode compartment is, therefore, preferably neutral.

The rate at which any metal will be deposited upon a supplementary cathode is a function of the relative distances between the main cathode and the anode and the supplementary cathode and the anode. This rate, therefore, may be regulated by moving the supplementary cathode closer to or farther away from the anode. It is, of course, understood that the current flowing through either the main cathode or a supplementary cathode may be regulated by other means such, for instance, as a rheostat.

If the rate of deposition of copper at the supplementary cathode is maintained sufficiently high so that the copper content of the anode electrolyte is maintained below about one-half of 1%, the copper will be deposited in powder form. The anode slime should preferably fall into a bag to keep slime and powdered copper separate. Copper in powder form highly desirable in many instances. It will enter into any reaction much more quickly. For instance, it may be oxidized to copper oxide by merely heating in the presence of air. The powdered copper may be collected and removed from the cell by any suitable means and after washing and drying it is ready for the market.

The nickel deposited at the cathode may be made removable therefrom by any suitable means and is also ready for the market as electrolytic nickel. Experiments have shown that nickel analyzing 99.9 plus may be made by this method.

While any suitable current density consistent with the results desired may be employed in the example given, it is found that a current density of 20 amperes per square foot is satisfactory.

The rate of flow through the diaphragms 16 and 17 should be sufficient to prevent the infiltration of ions coming from the anode. In the above example a rate of flow of about 1 gallon per hour per square foot of diaphragm surface is satisfactory.

It is found that the copper deposited at a supplementary cathode will contain some iron, if iron is present in the electrolyte. This iron, if in undesirable amounts, may be removed by previous purification of the electrolyte, or it may be removed from the deposited copper by purification of the same by any known method.

Any overflow from the box 11 may be recirculated and returned thereto inasmuch as this electrolyte is maintained in an uncontaminated condition. In view of its impoverishment of nickel and, of course, sulfate, it is advisable to bring it up by evaporation, or otherwise, to a higher concentration before returning it to the box 11.

As previously pointed out the overflow from the anode compartment may consist of iron, copper, cobalt and/or nickel sulfates. Cadmium sulphate and zinc sulphate may also be present if zinc and cadmium have not been previously removed from the anode, for instance, during casting of the same. This electrolyte which is considered contaminated, may be heated, for instance, to about C. The iron is then oxidized either by the additon of bleaching powder or by blowing air through the solution. This oxidizes any ferrous iron to ferric iron. Nickel carbonate slurry may then be added whereupon iron and copper are precipitated as carbonates and are filtered off. The nickel goes into solution as nickel sulfate. The filtrate, which is pure nickel sulfate, may then be fed back into the cathode compartment of the electrolytic cell. The filtrate, however, may contain cobalt if cobalt were present in the contaminated electrolyte. Cobalt may be separated from the filtrate by treating the same with chloride of lime, whereupon cobalt is precipitated as sesquioxide. Small amounts of cobalt may be deposited along with the nickel without objection.

The precipitates in each instance, as well as theanode slime, may be worked up by any known process for the recovery of the various constituents.

In the above example an anode of. unknown composition is employed. If the anode'is of a known composition the results may be very definitely predicted. Should the percentage of any particular metal be too high for most eflicient operation, it is, of course, possible to mix scrap metal taken from diiferent batches so as to lower the percentage of the particular metal in the mass which makes up the anode.

This process is, of course, in no'way limited to the electrodeposition of nickel and copper but may be applied to the electrodeposition of other metals. For instance, a zinc salt may be substituted for the nickel salt. We may, for instance, substitute a solution of zinc sulphate of approximately 5% metallic zinc as the cathode electrolyte. Or a solution of a cadmium salt, such, for instance, as cadmium sulphate having a concentration of about 10% metallic cadmium may be substituted as the cathode electrolyte. In either event it will be assumed that these metals have not been recovered from the anode by a casting or other process.

The regeneration of the electrolyte constituting the overflow from the anode compartment in either event maybe accomplished as follows. This overflow may contain soluble sulphates of the following metals: copper, nickel, cobalt, iron, zinc, manganese and cadmium. Scrap iron is added to this overflow to precipitate metallic copper. After filtering, the filtrate is oxidized with chloride of lime to convert any ferrous iron to ferric iron. The iron is then thrown down by means of powdered calcium carbonate. The temperature is somewhat raised during this reaction and may be, for instance, about 55 C. Manganese, if present, will drop out with the iron. The residue is a reddish brown powder containing chiefly ferric carbonate and a mixture of both ferrous and ferric hydrates. A composition of this character finds use in commerce as a brown paint pigment. Should manganese be present in considerable quantities it can be separated from the residue by means of the Well known basic acetate separation process.

The filtrate now contains the sulphates of nickel, cobalt, zinc and cadmium. This filtrate is further heated, for instance, to about C. and more calcium carbonate is added to precipitate zinc and cadmium as carbonates. Nickel and cobalt stay in solution as sulphates.

The residue of zinc and cadmium carbonates is dissolved in sulphuric acid. Metallic zinc is added to precipitate cadmium, leaving zinc sulphate in solution.

Assuming that zinc has been substituted for nickel in the example first given, this zinc sulphate is returned to the reaction.

If cadmium has been substituted for nickel in the example first given, the zinc and cadmium carbonates are not dissolved in sulphuric acid but are roasted to form oxides. of sulphuric acid insufllcient to dissolve both cadmium and zinc is then added. Inasmuch as cadmium oxide will be dissolved in preference A quantity" to zinc oxide, this quantity of sulphuric acid should be just sufiicient to dissolve the cadmium oxide, leaving zinc oxide as a residue. The filtrate, which is cadmium sulphate, may then be returned to the reaction.

The filtrate containing sulphates of nickel and cobalt is, of course, not discarded. The nickel and cobalt may be separated by means of the sesquioxide process and either sulphate may be returned to the cathode compartment of a separate electrolytic cell, depositing either metal at the cathode.

It is thus seen that the latter anode electro-j lyte regeneratingprocess may be employed for regenerating the electrolyte as zinc, cadmium, nickel or cobalt sulphate, depending upon the metal of the cathode electrolyte. Iron might be substituted for nickel although such a process may not be commercially feasible. In this event the iron residue above is taken up as sulphate, is purified by any known method, and returned to the cathode compartment.

The above illustrations include the deposition of nickel, cobalt, zinc, cadmium or iron at the cathode. In any of these cases, copper may or may not be deposited at the supplementary cathode as desired.

Any other method for regenerating the anode overflow may be employed without departing from the spirit of the invention.

Any soluble metallic salt may be substituted for a corresponding metallic salt in this process. For instance, we can substitute for any of the metallic sulphates enumerated any soluble metallic sulphate whose metal will be electrolytically deposited from a sulphuric acid electrolyte.

It is to be noted that nickel, cobalt, zinc, cadmium and iron are all electronegative with respect to copper in the electrolytic series for metallic sulphates. Any two metals may be separated in substantially pure form by using an alloy or mixture of such metals as the anode, supplying a relatively pure solution of a salt of the relatively electronegative metal to the cathode compartment so as to deposit said metal at the cathode, and supplying either a corresponding acid or a corresponding salt solution to the anode compartment. The relatively electropositive metal may be made to deposit preferentially at the supplementary cathode either in plate or in powder form by controlling the concentration of the metal in, and the acidity ofthe anode electrolyte according to known principles. The overflow from the anode compartment may be regenerated by any known method following the principles and objectives above set' The rate of overflow from the box 11 is immaterial inasmuch as no other compound will be present in the box 11 so long as the flow outwardly through the diaphragms is sufficient to form a barrier for the ions traveling in a directon from the anode to the cathode. The rate of overflow from the anode compartment, however, is important. Should the ion concentration in the anode compartment become abnormally high it is found that normal diffusion of the cathode electrolyte out through the diaphragms is insufiicient to form a complete barrier for these ions. By replenishing the anode electrolyte or adding the corresponding acid and permitting the excess electrolyte to flow out through the overflow, the ion concentration is kept sufiiciently low.

To guard against the accidental infiltration of ions from the anode into the cathode compartment, an inner compartment or box, shown at 25, having diaphragms 27 and 28, may be provided. Any other suitable construction may, of course, be substituted. The pressure differential is such that there is no flow of electrolyte into the anode compartment but merely from the cathode compartment into the spaces 26. Outlet 23 may be lowered to the dotted line position for this purpose. The cathode 18 is placed within this inner compartment 25 and a suitable solution, such as a Weak solution of sodium carbonate, is circulated through the spaces 26. This will tend to precipitate any of the free metals as carbonates. The inner compartment or box 25 may also be provided with an overflow if desired, as shown at 29. The precipitate may be removed from the spaces 26 by any suitable means such as by flushing with the circulating liquid or otherwise. This precipitate may consist of copper, iron, nickel and/or cobalt carbonates, and may be mixed with the overflow from the anode compartment and treated along with said overflow in the manner above'set forth.

By a proper circulation of the neutralizing solution in the spaces 26 any ions finding their way through diaphragms 16 and 1'7 may be carried from their path and removed with the solution. Because of the infinitely higher concentration of ions traveling from the cathode to the anode the flow of the latter will not be appreciably affected by this arrangement. Very good results may be obtained, for instance, by conducting the neutralizing solution at right angles to the path of the ions.

It is obvious that any other construction may be substituted for the boxes 11 and 25 and their respective parts and that the number of anodes, cathodes, supplementary cathodes, etc. may be varied without limit.

It is also obvious that the arrangement of the compartments may be reversed so that the anode, and if employed, the supplementary cathodes are in the box and the main cathode outside of the box. The box arrangement may, of course, be displaced by any other structure capable of a similar function.

It is, of course, understood that the concentration of ions from the anode in the spaces 26 would never attain a value sufficient to cause the same to pass through the diaphragms 2'7 and 28 of inner box, or compartment, 25.

It is obvious that this invention may be applied in a large variety of other Ways all of which will become apparent to persons skilled in the art upon becoming familiar with the description herein.

Having described the invention it is obvious that many modifications may be made in the same within the scope of the claims without departing from the spirit thereof.

We claim:

1-. A process for making metallic salts from a metallic mass of substantially unknown composition containing two known metals and for re covering said known metals in a substantially pure state, comprising forming an anode from said mass, electrolyzing said anode in a solution of soluble salts of the metals of said anode, segregating the cathode from the anode and providing means including a flow of electrolyte from said cathode toward said anode to prevent migration of ions from said anode to said cathode but permitting migration of ionsfrom said cathode to said anode, the electrolyte adjacent said cathode being a solution of a salt of the relatively electronegative of said 'known metals, maintaining the electrolyte adjacent said cathode in a substantially pure state and in a condition compatible with the deposition of its metal, providing a supplementary cathode removed from said first mentioned cathode, said supplementary cathode adapted for unrestricted interchange of ions with said anode, and maintaining the electrolyte adjacent said supplementary cathode in a condition compatible with the deposition of the other of said known metals.

2. A process for making metallic salts from a metallic mass of substantially unknown composition containing copper and one other known metal and for recovering said other known metal and said copper in a substantially pure state, comprising forming an anode from said mass, electrolyzing said anode in a solution of soluble saltsof the metals of said anode, segregating the cathode from the anode and providing means including a flow of electrolyte from said cathode toward said anode to prevent migration of ions from said anode to said cathode but permitting migration of ions from said cathode to said anode, the electrolyte adjacent said cathode being a substantially pure solution of a salt of said other known metal, maintaining the electrolyte adjacent said cathode in a substantially pure state and in a condition compatible with the deposition of said other known metal, providing a supplementary cathode removed from said first mentioned cathode, said supplementary cathode adapted for unrestricted interchange of ions with said anode, and maintaining the electrolyte adjacent said supplementary cathode in a condition compatible with the deposition of copper.

3. A process for making metallic salts from a metallic mass of substantially unknown composition containing copper and one other known metal and for recovering said other known metal and said copper in a substantially pure state,

comprising forming an anode from said mass, electrolyzing said anode in a solution of the soluble salts of the metals of said anode, segregating the cathode from the anode and providing means including a flow of electrolyte from said cathode toward said anode to prevent migration of ions from said anode to said cathode but per-' mitting migration of ions from said cathode to said anode, the electrolyte adjacent said cathode being a substantially pure solution of a salt of said other known metal, maintaining the electrolyte adjacent said cathode in a substantially pure state and in a condition compatible with the deposition of said other known metal, providing a supplementary cathode removed from said first mentioned cathode, said supple-- mentary cathode adapted for unrestricted interchange of ions with said anode, maintaining the electrolyte adjacent said supplementary cathode in a condition compatible with the deposition of copper, and regulating the rate of deposition of said copper so as to maintain the copper concentration of said electrolyte sufficiently low so that said copper will be deposited in powder form.

4. A process for separating any metal which is electronegative with respect to copper from copper comprising electrolyzing an anode comprising copper and said other metal in a solution of the salt of said other 'metal and copper, segregating the cathode from the anode, the electrolyte adjacent the cathode being a substantially pure solution of a salt of said other metal, maintaining the electrolyte adjacent the cathode in a substantially pure state, preventing the migration of ions from said anode to said cathode but permitting the migration of ions from said cathode to said anode, providing a supplementary cathode adapted for unrestricted interchange of ions with said anode, maintaining the electrolyte adjacent said supplementary cathode in a condition adapted to facilitate the deposition of copper, and maintaining the electrolyte adjacent said cathode in a condition adapted to facilitate the deposition of said other metal.

5. A process for separating any metal that is electronegative with respect to copper from copper comprising electrolyzing an anode comprising copper and said other metal in a solution of a salt of copper and of said other metal, segregating the cathode from the anode, the electrolyte adjacent the cathode being a substantially pure solution of a salt of said metal, maintaining the electrolyte adjacent the cathode in a substantially pure state, preventing the migration of ions from said anode to said cathode but permitting the migration of ions from said cathode to said anode, providing a supplementary cathode adapted for unrestricted interchange of ions with said anode, maintaining the electrolyte adjacent said supplementary cathode in a condition adapted to facilitate the deposition of copper, maintaining the electrolyte adjacent said cathode in a condition adapted to facilitate the deposition of said other metal, and regulating the rate of deposition of copper from said electrolyte so as to maintain the copper concentration of said electrolyte about said supplementary cathode at less than one-half of 1%.

6. A process for separating any metal that is electronegative with respect to copper from copper comprising electrolyzing an anode comprising copper and said other metal in a solution of a salt of said other metal and of copper, segregating the cathode from the anode, the electrolyte adjacent the cathode being a substantially pure solution of a salt of said other metal, maintaining the electrolyte adjacent the cathode in a substantially pure state, preventing the migration of ions from said anode to said cathode but permitting the migration of ions from said cathode to said anode, providing a supplementary cathode adapted for unrestricted interchange of ions with said anode, maintaining the electrolyte adjacent said supplementary cathode in a condition adapted to facilitate the deposition of copper, maintaining the electrolyte adjacent said cathode in a condition adapted to facilitate the deposition of said other metal, regulating the rate of deposition of copper from said elbctrolyte so as to maintain the copper concentration of said electrolyte about said supplementary cathode at less than one-half of 1%, regenerating the electrolyte about said anode and returning said regenerated electrolyte to said reaction.

7. An electrolytic cell comprising an anode, a cathode, means for preventing migration of ions from said anode to said cathode but permitting migration of ions from said cathode to said anode, and a supplementary cathode adapted for unrestricted interchange of ionswith said anode.

8. In a process of the kind described, the step of preventing migration of ions from the anode to the cathode but permitting migration of ions from the cathode to the anode, comprising interposing spaced pervious diaphragms in the path of said ions, circulating a neutralizing liquid between said diaphragms at an angle to said path, said neutralizing liquid adapted to remove from the reaction ions migrating from said anode toward said cathode and maintaining a pressure differential between the electrolyte surrounding the cathode and the liquid between said diaphragms.

9. An electrolytic cell comprising an anode, a cathode, means for preventing migration of ions from said anode to said cathode but permitting migration of ions from said cathode to said anode, said means including means for circulating a desired liquid through the path of said ions and at an angle thereto, and a supplementary cathode adapted for unrestricted interchange of ions with said anode.

WILLIAM P. l-lElNEKEN. MEYER L. FREED. 

